What could I improve on on my monkey model?
JUST SOME TIPS: The body part topology of your model is decent, though hands and legs' topology is too dense. Try to keep it as simple as it can be (start to model fingers using a circle with only 8 vertices).


Do the same for the toes (see my topology suggestion below).



Always start with a simpliest shapes and then slowly add more geometry.
Your question reminds me this one: How to retopologize my model? Wish I have more time right now to retopologize this model for you and show you some simple solutions, but I'm quite busy right now :(.

Remember, that simple and smart topology is a key to make the model bend well while animating (simple finger model topology bend example here: How do rigs relate to weights?)